CsREV-CsTCP4-CsVND7 module shapes xylem patterns differentially between stem and leaf to enhance tea plant tolerance to drought.

Cultivating drought-tolerant tea varieties enhances both yield and quality of tea plants in northern China. However, the mechanisms underlying their drought tolerance remain largely unknown. Here we identified a key regulator called CsREV, which differentially regulates xylem patterns between leaves and stems, thereby conferring drought tolerance in tea plants. When drought occurs, upregulation of CsREV activates the CsVND7a-dependent xylem vessel differentiation. However, when drought persists, the vessel differentiation is hindered as CsVND7a is downregulated by CsTCP4a. This, combined with the CsREV-promoted secondary-cell-wall thickness of xylem vessel, leads to the enhanced curling of leaves, a characteristic closely associated with plant drought tolerance. Notably, this inhibitory effect of CsTCP4a on CsVND7a expression is absent in stems, allowing stem xylem vessels to continuously differentiate. Overall, the CsREV-CsTCP4-CsVND7 module is differentially utilized to shape the xylem patterns in leaves and stems, potentially balancing water transportation and utilization to improve tea plant drought tolerance.

A Pectate Lyase Gene Plays a Critical Role in Xylem Vascular Development in Arabidopsis.

As a major component of the plant primary cell wall, structure changes in pectin may affect the formation of the secondary cell wall and lead to serious consequences on plant growth and development. Pectin-modifying enzymes including pectate lyase-like proteins (PLLs) participate in the remodeling of pectin during organogenesis, especially during fruit ripening. In this study, we used Arabidopsis as a model system to identify critical PLL genes that are of particular importance for vascular development. Four PLL genes, named AtPLL15, AtPLL16, AtPLL19, and AtPLL26, were identified for xylem-specific expression. A knock-out T-DNA mutant of AtPLL16 displayed an increased amount of pectin, soluble sugar, and acid-soluble lignin (ASL). Interestingly, the atpll16 mutant exhibited an irregular xylem phenotype, accompanied by disordered xylem ray cells and an absence of interfascicular phloem fibers. The xylem fiber cell walls in the atpll16 mutant were thicker than those of the wild type. On the contrary, AtPLL16 overexpression resulted in expansion of the phloem and a dramatic change in the xylem-to-phloem ratios. Altogether, our data suggest that AtPLL16 as a pectate lyase plays an important role during vascular development in Arabidopsis.

Visualization of phosphorus re-translocation and phosphate transporter expression profiles in a shortened annual cycle system of poplar.

Phosphorus (P) is an essential macronutrient for plant growth. In deciduous trees, P is remobilized from senescing leaves and stored in perennial tissues during winter for further growth. Annual internal recycling and accumulation of P are considered an important strategy to support the vigorous growth of trees. However, the pathways of seasonal re-translocation of P and the molecular mechanisms of this transport have not been clarified. Here we show the seasonal P re-translocation route visualized using real-time radioisotope imaging and the macro- and micro-autoradiography. We analysed the seasonal re-translocation P in poplar (Populus alba. L) cultivated under 'a shortened annual cycle system', which mimicked seasonal phenology in a laboratory. From growing to senescing season, sink tissues of 32 P and/or 33 P shifted from young leaves and the apex to the lower stem and roots. The radioisotope P re-translocated from a leaf was stored in phloem and xylem parenchyma cells and redistributed to new shoots after dormancy. Seasonal expression profile of phosphate transporters (PHT1, PHT5 and PHO1 family) was obtained in the same system. Our results reveal the seasonal P re-translocation routes at the organ and tissue levels and provide a foothold for elucidating its molecular mechanisms.

Profiling of widely targeted metabolomics for the identification of chemical composition in epidermis, xylem and pith of Gleditsiae Spina.

Gleditsiae Spina, the thorn of Gleditsia sinensis Lam., has a long history of being used as a traditional medicine in East Asian countries. However, only a few biologically active substances have been identified from it. In this study, the epidermis, xylem and pith of Gleditsiae Spina, respectively Gs-E, Gs-X and Gs-P, were studied. We used a widely targeted metabolomics method to investigate the chemical composition of Gs-E, Gs-X and Gs-P. A total of 728 putative metabolites were identified from Gleditsiae Spina, including 211 primary metabolites and 517 secondary metabolites. These primary and secondary metabolites could be categorized into more than 10 different classes. Flavonoids, phenolic acids, lipids, amino acids and derivatives, and organic acids constituted the main metabolite groups. Multivariate statistical analysis showed that the Gs-E, Gs-X and Gs-P samples could be clearly separated. Differential accumulated metabolite (DAM) analysis revealed that more than half of the DAMs exhibited the highest relative concentrations in Gs-E, and most of the DAMs showed the lowest relative concentrations in Gs-X. Moreover, 11 common differential primary metabolites and 79 common differential secondary metabolites were detected in all comparison groups. These results further our understanding of chemical composition and metabolite accumulation of Gleditsiae Spina.

The plant axis as the command centre for (re)distribution of sucrose and amino acids.

Along with the increase in size required for optimal colonization of terrestrial niches, channels for bidirectional bulk transport of materials in land plants evolved during a period of about 100 million years. These transport systems are essentially still in operation - though perfected over the following 400 million years - and make use of hydrostatic differentials. Substances are accumulated or released at the loading and unloading ends, respectively, of the transport channels. The intermediate stretch between the channel termini is bifunctional and executes orchestrated release and retrieval of solutes. Analyses of anatomical and physiological data demonstrate that the release/retrieval zone extends deeper into sources and sinks than is commonly thought and covers usually much more than 99% of the translocation stretch. This review sketches the significance of events in the intermediate stretch for distribution of organic materials over the plant body. Net leakage from the channels does not only serve maintenance and growth of tissues along the pathway, but also diurnal, short-term or seasonal storage of reserve materials, and balanced distribution of organic C- and N-compounds over axial and terminal sinks. Release and retrieval are controlled by plasma-membrane transporters at the vessel/parenchyma interface in the contact pits along xylem vessels and by plasma-membrane transporters at the interface between companion cells and phloem parenchyma along sieve tubes. The xylem-to-phloem pathway vice versa is a bifacial, radially oriented system comprising a symplasmic pathway, of which entrance and exit are controlled at specific membrane checkpoints, and a parallel apoplasmic pathway. A broad range of specific sucrose and amino-acid transporters are deployed at the checkpoint plasma membranes. SUCs, SUTs, STPs, SWEETs, and AAPs, LTHs, CATs are localized to the plasma membranes in question, both in monocots and eudicots. Presence of Umamits in monocots is uncertain. There is some evidence for endo- and exocytosis at the vessel/parenchyma interface supplementary to the transporter-mediated uptake and release. Actions of transporters at the checkpoints are equally decisive for storage and distribution of amino acids and sucrose in monocots and eudicots, but storage and distribution patterns may differ between both taxa. While the majority of reserves is sequestered in vascular parenchyma cells in dicots, lack of space in monocot vasculature urges "outsourcing" of storage in ground parenchyma around the translocation path. In perennial dicots, specialized radial pathways (rays) include the sites for seasonal alternation of storage and mobilization. In dicots, apoplasmic phloem loading and a correlated low rate of release along the path would favour supply with photoassimilates of terminal sinks, while symplasmic phloem loading and a correlated higher rate of release along the path favours supply of axial sinks and transfer to the xylem. The balance between the resource acquisition by terminal and axial sinks is an important determinant of relative growth rate and, hence, for the fitness of plants in various habitats. Body enlargement as the evolutionary drive for emergence of vascular systems and mass transport propelled by hydrostatic differentials.

Comparative effectiveness of Se translocation between low-Se and high-Se rice cultivars under Se fertilization.

The production of natural selenium (Se)-rich food by using a high-Se crop cultivar is beneficial to human health and environmental safety; however, the underlying mechanism of different Se-accumulation ability between high- and low-Se rice cultivars remains unclear. A low-grain-Se cultivar and high-grain-Se cultivar of rice were used as test materials, and two levels of Se (0 and 0.5 mg kg-1) were arranged in a randomized design containing twelve replicates. The dynamic changes of shoot Se concentration and accumulation, xylem sap Se concentration, shoot and grain Se distribution, Se transporters genes (OsPT2, Sultr1;2, NRT1.1B) expression of the high- and low-Se rice cultivars were determined. The shoot Se concentration and accumulation of the high-Se rice showed a greater degree of reduction than those of the low-Se rice during grain filling stage, indicating that leaves of high-Se rice served as a Se source and supplied more Se for the growth centre grain. The expression levels of OsPT2, NRT1.1B and Sultr1;2 in the high-Se rice cultivar were significantly higher than those in the low-Se rice cultivar, which indicated that the high-Se rice cultivar possessed better transport carriers. The distribution of Se in grain of the high-Se rice cultivar was more uniform, whereas the low-Se cultivar tended to accumulate Se in embryo end. The stronger reutilization of Se from shoots to grains promoted by increased transporters genes expression and optimized grain storage space may explain how the high-Se rice cultivar is able to accumulate more Se in grain.

Phosphorus deficiency induces root proliferation and Cd absorption but inhibits Cd tolerance and Cd translocation in roots of Populus × euramericana.

To disclose how phosphorus deficiency influence phytoremediation of Cd contamination using poplars, root architecture, Cd absorption, Cd translocation and antioxidant defense in poplar roots were investigated using a clone of Populus × euramericana. Root growth was unaltered by Cd exposure regardless of P conditions, while the degree of root proliferation upon P deficiency was changed by high level of Cd exposure. The concentration and content of Cd accumulation in roots were increased by P deficiency. This can be partially explained by the increased expression of genes encoding PM H + -ATPase under the combined conditions of P deficiency and high Cd exposure, which enhanced Cd2+-H+ exchanges and led to an increment of Cd uptake under P deficiency. Despite of the increasing Cd accumulation in roots, the translocation of Cd from roots to aerial tissues sharply decreased upon P deficiency. The relative expression of genes responsible for Cd translocation (HMA4) decreased upon P deficiency and thus inhibited Cd translocation via xylem. GR activity was decreased by P deficiency, which can inhibit the form of GSH and GSH-Cd complexes and decrease Cd translocation via GSH-Cd complexes. The transportation of PC-Cd complexes into vacuole decreased under P deficiency as a result of the low expression of PCS and ABCC1, and thus suppressed Cd tolerance and Cd detoxification in roots. Moreover, P deficiency decreased the levels of antioxidase (GR and CAT) and phytohormones including JA, ABA and GA3, which synchronously reduced antioxidant capacity in roots.

LaALMT1 mediates malate release from phosphorus-deficient white lupin root tips and metal root to shoot translocation.

Under phosphorus (P) deficiency, Lupinus albus (white lupin) releases large amounts of organic acid anions from specialized root structures, so-called cluster or proteoid roots, to mobilize and acquire sparingly soluble phosphates from a restricted soil volume. The molecular mechanisms underlying this release and its regulation are, however, poorly understood. Here, we identified a gene belonging to the aluminium (Al)-activated malate transporter (ALMT) family that specifically contributes to malate, but not citrate release. This gene, LaALMT1, was most prominently expressed in the root apices under P deficiency, including those of cluster roots and was also detected in the root stele. Contrary to several ALMT homologs in other species, the expression was not stimulated, but moderately repressed by Al. Aluminium-independent malate currents were recorded from the plasma membrane localized LaALMT1 expressed in Xenopus oocytes. In composite lupins with transgenic roots, LaALMT1 was efficiently mutated by CRISPR-Cas9, leading to diminished malate efflux and lower xylem sap malate concentrations. When grown in an alkaline P-deficient soil, mutant shoot phosphate concentrations were similar, but iron and potassium concentrations were diminished in old leaves, suggesting a role for ALMT1 in metal root to shoot translocation, a function that was also supported by growth in hydroponics.

Positron-emitting tracer imaging of fluoride transport and distribution in tea plant.

BACKGROUND: Tea (Camellia sinensis (L.) O. Kuntze) is a hyper-accumulator of fluoride (F). To understand F uptake and distribution in living plants, we visually evaluated the real-time transport of F absorbed by roots and leaves using a positron-emitting (18 F) fluoride tracer and a positron-emitting tracer imaging system. RESULTS: F arrived at an aerial plant part about 1.5 h after absorption by roots, suggesting that tea roots had a retention effect on F, and then was transported upward mainly via the xylem and little via the phloem along the tea stem, but no F was observed in the leaves within the initial 8 h. F absorbed via a cut petiole (leaf 4) was mainly transported downward along the stem within the initial 2 h. Although F was first detected in the top and ipsilateral leaves, it was not detected in tea roots by the end of the monitoring. During the monitoring time, F principally accumulated in the node. CONCLUSION: F uptake by the petiole of excised leaf and root system was realized in different ways. The nodes indicated that they may play pivotal roles in the transport of F in tea plants. © 2020 Society of Chemical Industry.

Morphological and physiological responses of the potato stem transport tissues to dehydration stress.

MAIN CONCLUSION: Adaptation of the xylem under dehydration to smaller sized vessels and the increase in xylem density per stem area facilitate water transport during water-limiting conditions, and this has implications for assimilate transport during drought. The potato stem is the communication and transport channel between the assimilate-exporting source leaves and the terminal sink tissues of the plant. During environmental stress conditions like water scarcity, which adversely affect the performance (canopy growth and tuber yield) of the potato plant, the response of stem tissues is essential, however, still understudied. In this study, we investigated the response of the stem tissues of cultivated potato grown in the greenhouse to dehydration using a multidisciplinary approach including physiological, biochemical, morphological, microscopic, and magnetic resonance imaging techniques. We observed the most significant effects of water limitation in the lower stem regions of plants. The light microscopy analysis of the potato stem sections revealed that plants exposed to this particular dehydration stress have higher total xylem density per unit area than control plants. This increase in the total xylem density was accompanied by an increase in the number of narrow-diameter xylem vessels and a decrease in the number of large-diameter xylem vessels. Our MRI approach revealed a diurnal rhythm of xylem flux between day and night, with a reduction in xylem flux that is linked to dehydration sensitivity. We also observed that sink strength was the main driver of assimilate transport through the stem in our data set. These findings may present potential breeding targets for drought tolerance in potato.

Oxylipins Other Than Jasmonic Acid Are Xylem-Resident Signals Regulating Systemic Resistance Induced by Trichoderma virens in Maize.

Multiple long-distance signals have been identified for pathogen-induced systemic acquired resistance, but mobile signals for symbiont-induced systemic resistance (ISR) are less well understood. We used ISR-positive and -negative mutants of maize (Zea mays) and the beneficial fungus Trichoderma virens and identified 12-oxo-phytodienoic acid (12-OPDA) and α-ketol of octadecadienoic acid (KODA) as important ISR signals. We show that a maize 13-lipoxygenase mutant, lox10, colonized by the wild-type T. virens (TvWT) lacked ISR response against Colletotrichum graminicola but instead displayed induced systemic susceptibility. Oxylipin profiling of xylem sap from T. virens-treated plants revealed that 12-OPDA and KODA levels correlated with ISR. Transfusing sap supplemented with 12-OPDA or KODA increased receiver plant resistance in a dose-dependent manner, with 12-OPDA restoring ISR of lox10 plants treated with TvWT or T. virens Δsm1, a mutant unable to induce ISR. Unexpectedly, jasmonic acid (JA) was not involved, as the JA-deficient opr7 opr8 mutant plants retained the capacity for T. virens-induced ISR. Transcriptome analysis of TvWT-treated maize B73 revealed upregulation of 12-OPDA biosynthesis and OPDA-responsive genes but downregulation of JA biosynthesis and JA response genes. We propose a model that differential regulation of 12-OPDA and JA in response to T. virens colonization results in ISR induction.

Cytosolic Acetyl-CoA Generated by ATP-Citrate Lyase Is Essential for Acetylation of Cell Wall Polysaccharides.

Plant cell wall polysaccharides, including xylan, glucomannan, xyloglucan and pectin, are often acetylated. Although a number of acetyltransferases responsible for the acetylation of some of these polysaccharides have been biochemically characterized, little is known about the source of acetyl donors and how acetyl donors are translocated into the Golgi, where these polysaccharides are synthesized. In this report, we investigated roles of ATP-citrate lyase (ACL) that generates cytosolic acetyl-CoA in cell wall polysaccharide acetylation and effects of simultaneous mutations of four Reduced Wall Acetylation (RWA) genes on acetyl-CoA transport into the Golgi in Arabidopsis thaliana. Expression analyses of genes involved in the generation of acetyl-CoA in different subcellular compartments showed that the expression of several ACL genes responsible for cytosolic acetyl-CoA synthesis was elevated in interfascicular fiber cells and induced by secondary wall-associated transcriptional activators. Simultaneous downregulation of the expression of ACL genes was demonstrated to result in a substantial decrease in the degree of xylan acetylation and a severe alteration in secondary wall structure in xylem vessels. In addition, the degree of acetylation of other cell wall polysaccharides, including glucomannan, xyloglucan and pectin, was also reduced. Moreover, Golgi-enriched membrane vesicles isolated from the rwa1/2/3/4 quadruple mutant were found to exhibit a drastic reduction in acetyl-CoA transport activity compared with the wild type. These findings indicate that cytosolic acetyl-CoA generated by ACL is essential for cell wall polysaccharide acetylation and RWAs are required for its transport from the cytosol into the Golgi.

Transcriptomic and metabolomic analyses reveal several critical metabolic pathways and candidate genes involved in resin biosynthesis in Pinus massoniana.

Pine resin, which typically consists of terpenoids, is a natural product used in various industrial applications. Oleoresin can be obtained from the xylem tissue by wounding the stem bark. Pinus massoniana (masson pine) is an important resin-tapping tree species that originated in southern China. Masson pines with different genetic backgrounds typically have different resin-yielding capacities (RYCs). However, the mechanisms underlying high resin yield in masson pines are unclear. The aim of this study was to identify the possible genetic regulation pathways and functional genes that influence the resin yield. In this study, we conducted transcriptomic and metabolomic studies of masson pine secondary xylem with high, medium, and low RYCs. A total of 230,068 unigenes and 3894 metabolites were identified from the tissue of the secondary xylem. Several differentially expressed regulation factors, including WRKY, bHLH, and ERF, and functional genes such as PKc and LRR-RLKs, were identified among these masson pines. The Kyoto Encyclopedia of Genes and Genomes pathways were mainly focused on diterpenoid biosynthesis, plant hormone signal transduction, and ABC transporters. Furthermore, integration of the transcriptomic and metabolomic data indicated that the PKc- and LRR-RLK-related regulatory and metabolic pathways may play critical roles in the biosynthesis of terpenoids. These above results improve our understanding of the biosynthesis mechanism of oleoresin in P. massoniana and facilitate further research work into the functional analysis of these candidate genes.

Characterization of Chemical Component Variations in Different Growth Years and Tissues of Morindae Officinalis Radix by Integrating Metabolomics and Glycomics.

Morindae Officinalis Radix (MOR), the dried root of Morinda officinalis F.C. How (Rubiaceae), is a popular food supplement in southeastern China for bone protection, andrological, and gynecological healthcare. In clinical use, 3-4 year old MOR is commonly used and the xylem is sometimes removed. However, there is no scientific rationale for these practices so far. In this study, metabolomics and glycomics were integrated using multiple chromatographic and mass spectrometric techniques coupled with multivariate statistical analysis to investigate the qualitative and quantitative variations of secondary metabolome and glycome in different growth years (1-7 years) and tissues (xylem and cortex) of MOR. The results showed that various types of bioactive components reached a maximum between 3 and 4 years of growth and that the xylem contained more potentially toxic constituents but less bioactive components than the cortex. This study provides the chemical basis for the common practice of using 3-4 year old MOR with the xylem removed.

An improved centrifuge method for determining water extraction curves and vulnerability curves in the long-vessel species Robinia pseudoacacia.

Significant improvements to the centrifuge water-extraction method of measuring the percentage loss volume of water (PLV) and corresponding vulnerability curves (VCs) are reported. Cochard and Sperry rotors are both incapable of measuring the VCs of species with long vessels because of premature embolism induced by hypothetical nanoparticles that can be drawn into segments during flow measurement. In contrast, water extraction pushes nanoparticles out of the sample. This study focuses on a long-vessel species, Robinia pseudoacacia, for which many VCs have been constructed by different methods, and the daily water relations have been quantified. PLV extraction curves have dual Weibull curves, and this paper focuses on the second Weibull curve because it involves the extraction of water from vessels, as proven by staining methods. We demonstrate an improved water extraction method after evaporation correction that has accuracy to within 0.5%, shows good agreement with two traditional methods that are slower and less accurate, and is immune to nanoparticle artefacts. Using Poiseuille's Law and the geometry of vessels, we argue that the percentage loss of conductivity (PLC) equals 2PLV-PLV2 in a special case where all vessels, regardless of size, have the same vulnerability curve. In this special case, this equation predicts the data reasonably well.

Effect of selenium on the subcellular distribution of cadmium and oxidative stress induced by cadmium in rice (Oryza sativa L.).

Cadmium (Cd) is absorbed readily by rice plants and is transferred to humans when contaminated rice is consumed. Adding selenium (Se) to the plant nutrient solutions reduces the accumulation of Cd in the rice (Oryza sativa L.) seedlings. However, as the relevant underlying mechanism remains unclear, the aim of our study was to improve our understanding of the Se-mediated resistance to Cd stress in rice. We conducted hydroponic experiments to study the effects of selenite or selenate on Cd subcellular distribution and xylem transport in rice seedlings under Cd stress, and we investigated the antioxidative defense responses in the rice plants. We found that the supplementation of both Se forms decreased the Cd accumulations in the roots and shoots of the rice plants. The selenite addition significantly decreased the Cd contents in different subcellular fractions of the rice roots, increased the proportion of Cd distributed to soluble cytosol by 23.41%, and decreased the Cd distribution in the organelle by 28.74% in contrast with the treatment with Cd only. As regards the selenate addition, only the Cd distribution ratio of cytosol was increased by 13.07%. After adding selenite, a decrease of 55.86% in the Cd concentration in xylem sap was observed, whereas little change was found after treatment co-applied with selenate. The hydrogen peroxide (H2O2) and malondialdehyde(MDA) contents in the rice roots were elevated under Cd stress, and the addition of selenite and selenate decreased the H2O2 levels by 77.78% and 59.26%, respectively. Co-exposure to Cd and Se elevated the glutathione (GSH) accumulations in the rice shoots and roots, with the degree of increase being the following: co-applied with selenite > co-applied with selenate > Cd alone treatment. Exposure to Cd increased the catalase (CAT) activity in the roots significantly, whereas it decreased in the shoots. After selenite or selenate supplementation, the CAT activity in the rice roots increased compared with applying only Cd. Compared with the control, the addition of Cd or Se had no significant effect on the activities of peroxidase (POD) or ascorbate peroxidase (APX). Our results showed that Se affected the Cd accumulation in rice seedlings by altering the Cd subcellular distribution and decreasing the ROS induced by Cd stress. Such effects were more significant in the selenite than in the selenate applied treatment.

A Method to Study the Distribution Patterns for Metabolites in Xylem and Phloem of Spatholobi Caulis.

Spatholobi Caulis (SC), the vine stem of Spatholobus suberectus Dunn, is a widely used traditional Chinese medicine (TCM) for the treatment of blood stasis syndrome and related diseases. Xylem and phloem are the main structures of SC and the color of xylem in SC is red brown or brown while the phloem with resin secretions is reddish brown to dark brown. They are alternately arranged in a plurality of concentric or eccentric rings. In order to investigate the distribution patterns of metabolites in xylem and phloem of SC, an analytical method based on UFLC-QTRAP-MS/MS was established for simultaneous determination of 22 constituents including four flavanols, nine isoflavones, two flavonols, two dihydroflavones, one flavanonol, one chalcone, one pterocarpan, one anthocyanidin and one phenolic acid in the samples (xylem and phloem) from Laos. Furthermore, according to the contents of 22 constituents, heat map, principal components analysis (PCA), orthogonal partial least squares discriminant analysis (OPLS-DA) and t-test were used to evaluate the samples and discover the differences between xylem and phloem of SC. The results indicated that the measured ingredients in xylem and phloem were significantly different. To be specific, the contents of flavonoids in xylem were higher than that in phloem, while the content of protocatechuic acid showed a contrary tendency. This study will not only reveal the distribution patterns of metabolites in xylem and phloem of SC but also facilitate further study on their quality formation.

A pair of phospho-base methyltransferases important for phosphatidylcholine biosynthesis in Arabidopsis.

Phosphatidylcholine (PtdCho) is a predominant membrane lipid class in eukaryotes. Phospho-base N-methyltransferase (PMT) catalyzes a critical step in PtdCho biosynthesis. However, in Arabidopsis thaliana, the discovery of involvement of the specific PMT isoform in PtdCho biosynthesis remains elusive. Here, we show that PMT1 and PMT3 redundantly play an essential role in phosphocholine (PCho) biosynthesis, a prerequisite for PtdCho production. A pmt1 pmt3 double mutant was devoid of PCho, which affected PtdCho biosynthesis in vivo, showing severe growth defects in post-embryonic development. PMT1 and PMT3 were both highly expressed in the vasculature. The pmt1 pmt3 mutants had specifically affected leaf vein development and showed pale-green seedlings that were rescued by exogenous supplementation of PCho. We suggest that PMT1 and PMT3 are the primary enzymes for PCho biosynthesis and are involved in PtdCho biosynthesis and vascular development in Arabidopsis seedlings.

Comparison of foliar silicon and selenium on cadmium absorption, compartmentation, translocation and the antioxidant system in Chinese flowering cabbage.

Silicon (Si) and selenium (Se) are beneficial for many higher plants when grown on stress conditions. However, the mechanisms underlying the differential effects between foliar Si and Se in alleviation of plant toxicity exposed to cadmium (Cd) stress are remained unclear. In this study, we investigated the discrepant mechanisms of foliar Si and Se on Cd absorption and compartmentation by roots, its translocation in xylem, and the antioxidant system within Chinese flowering cabbage (Brassica campestris L. ssp. chinensis var. utilis) under low and high Cd stress. Results showed that plant growth was significantly enhanced by foliar additions of Si or/and Se according to an increased plant tissue biomass at high Cd exposure. In addition, the foliar coupled addition of Si and Se showed little effects on the concentrations of Si or Se in plant tissues in comparison with the single addition of foliar Si or Se respectively. The foliar Si alone or combined with Se markedly reduced the Cd concentrations in plant shoots under two Cd treatments. This might be explained by the lower Cd concentrations in symplast and apoplast and the higher Cd concentrations in cell walls of plant roots, and the lower Cd concentrations in xylem sap. However, no great changes in these values were observed under the treatments of foliar Se alone. Moreover, the foliar additions of Si or/and Se all increased the antioxidant enzyme activities of SOD, CAT and APX in plant tissues, especially at high Cd dosage. No significant differences in the increasing degrees of these three antioxidant enzymes were found between the foliar Si and Se treatments. However, only the foliar Se alone or combined with Si markedly promoted the antioxidant enzyme activities of GR and DHAR in plant tissues. Our findings demonstrate that the alleviation of Cd toxicity by foliar Si maybe mainly responsible for inhibition of Cd absorption and its translocation to plant shoots, reinforcing its compartmentation into root cell walls, whilst enhancing the antioxidant enzyme system may be employed by foliar Se.

The water relations and xylem attributes of albino redwood shoots (Sequioa sempervirens (D. Don.) Endl.).

Plants that lack chlorophyll are rare and typically restricted to holoparasites that obtain their carbon, water and mineral resources from a host plant. Although not parasites in the traditional sense, albino foliage, such as the sprouts that sometimes develop from redwood tree trunks, are comparable in function. They occur sporadically, and can reach the size of shrubs and in rare cases, trees. Albino redwoods are interesting because in addition to their reduced carbon resources, the absence of chloroplasts may impede proper stomatal function, and both aspects may have upstream consequences on water transport and xylem quality. We examined the water relations, water transport and xylem anatomical attributes of albino redwoods and show that similar to achlorophyllous and parasitic plants, albino redwoods have notably higher stomatal conductance than green sprouts. Given that stem xylem tracheid size as well as water transport efficiency are nearly equivalent in both albino and green individuals, we attribute the increased leaf water loss in albino sprouts to lower leaf to xylem area ratios, which favour improved hydration relative to green sprouts. The stems of albino redwoods were more vulnerable to drought-induced embolism than green stems, and this was consistent with the albino's weaker tracheids, as characterized by wall thickness to lumen diameter measures. Our results are both complementary and consistent with previous research on achlorophyllous plants, and suggest that the loss of stomatal control and photosynthetic capacity results in substantial vascular and anatomical adjustments.